In the field of magnetic recording/reproduction apparatuses, there is a trend towards the use of higher recording densities with the aim of producing small, high-capacity apparatuses. A representative example of a magnetic recording/reproduction apparatus is a hard disk drive. Hard disk drives with areal recording densities in excess of 10 GBit/in2 already have appeared on the market, with 20 Gbit/in2 drives being expected in the next few years due to the rapid technological advancements being made in this field.
A major factor in the achievement of high recording densities is the use of magneto-resistive type heads that allow increases in linear recording density and can reproduce, with a favorable S/N ratio, a signal recorded on a track no wider than a few microns.
The increases in recording density also have made it necessary to reduce the distance that a floating magnetic slider floats above the surface of a magnetic disk. This increases the probability of the slider colliding with the disk due to a variety of causes. Such a situation requires that magnetic disks be made with smoother surfaces.
Tracking servo technology used in a head also plays an important role in having a head precisely follow a narrow track. Modern hard disk drives that use such tracking servo technology have areas in which tracking servo signals, address information signals, reproduction clock signals and the like are recorded that are provided on magnetic recording media at intervals of a predetermined angle, (also called “preformat recording areas” in the following). A drive apparatus detects the position of the head from the above signals that are outputted by the head at predetermined time intervals, and corrects the head position so that the head can properly follow a track on the disk.
The servo signals, address information signals and reproduction clock signals therefore are used as reference signals in order to have the head properly scan tracks on the disk. As a result, high positional accuracy is required when writing these signals onto a disk (such writing is hereafter referred to as “formatting” the disk). For current hard disk drives, the recording head is positioned during formatting using a dedicated servo apparatus equipped with a highly precise position detecting apparatus that uses optical interference (hereafter such servo apparatuses are referred to as “servo writers”).
However, formatting using an aforementioned servo writer has the following drawbacks.
Firstly, recording by a magnetic head is linear recording where there is relative movement between the magnetic head and the magnetic recording medium. Since it is necessary to record signals on a large number of tracks, preformatting using a servo writer takes a long time. To make manufacturing more efficient, several expensive, dedicated servo writers need to be provided, making the preformatting operation very costly.
Secondly, the implementation and maintenance of many servo writers incurs a high cost. This cost becomes more severe as the track density and number of tracks increase.
As a result, a different formatting method that does not use servo writers has been proposed. With this method, a disk called a “master” on which all of the servo information is recorded is placed on top of the magnetic disk to be formatted and energy to achieve transfer is applied from an external source to transfer all of the master information onto the magnetic disk.
One example of this technique is the magnetic recording apparatus taught by Publication of Unexamined Japanese Patent Application JP H10-40544A. According to this application, a magnetic portion made from a ferromagnetic material is formed in a pattern corresponding to an information signal on a substrate surface, thereby producing a master information carrier. The surface of this master information carrier is brought into contact with the surface of a magnetic recording medium. This magnetic recording medium may be in the form of a sheet or a disk, and is provided with a ferromagnetic thin film or an applied layer of a ferromagnetic powder. A predetermined magnetic field is then applied, so that a magnetic pattern corresponding to the information signals formed on the master information carrier is recorded on the magnetic recording medium.
With the above method, the arrangement of patterns corresponding to the information signals on the master information carrier can be recorded simultaneously onto the magnetic recording medium as magnetic patterns. When recording information signals using this kind of magnetic transfer apparatus, it is important to have the information signals recorded uniformly and with high stability across the entire surface of the magnetic recording medium. However, when unwanted protrusions or foreign matter are present at the interface of the magnetic recording medium and the master information carrier, depressions appear in the surface of the magnetic recording medium when the magnetic recording medium comes into contact with the master information carrier.
FIG. 18 shows a graph produced by measuring a cross-section of a depression appearing after the magnetic recording medium and master information carrier have been brought into contact and magnetic transfer has been carried out with a conventional magnetic transfer method. As shown in FIG. 18, the depression is about 50 nm deeper than the surface of the magnetic recording medium, and is surrounded by a slight protrusion that is about 20 nm high.
A floating magnetic slider generally floats about 20 nm above the surface of a magnetic recording medium. If, like the medium shown in FIG. 18, a magnetic recording medium has protrusions that are 20 nm high, the magnetic head will come into contact with the magnetic recording medium during the recording and reproduction of data. When this happens, the impact forces the magnetic head upward, increasing the clearance between the magnetic head and the magnetic recording medium and worsening the signal recording/reproduction performance. Also, physical contact between the magnetic head and the magnetic recording medium shortens the life of the magnetic head and can lead to disk failures for the magnetic recording medium.
FIG. 19 is a depiction of the measurements produced by optically measuring protrusions across the entire surface of a magnetic recording medium on which information has been magnetically transferred using a conventional magnetic transfer method. As can be seen, a large number of protrusions 20 nm or higher are present on the surface of the magnetic recording medium.
As described above, magnetic transfer according to conventional magnetic transfer methods often results in a large number of protrusions being present on the magnetic disk after the magnetic transfer. This causes the problems of lower recording/reproduction performance of the magnetic recording medium and a shorter lifespan for a magnetic head. If the moves towards higher recording densities are accompanied by a reduction in the distance that a magnetic head floats above a magnetic recording medium, these problems will become more severe.